Power control generally relates to the issue of determining and assigning transmit power for radio transmissions in a wireless network. By way of example, power control is used for dynamically adjusting the transmit power of base stations such as eNBs and wireless devices such as UEs based on variations of the channel quality and so forth to achieve and maintain a desired Quality of Service, QoS, reduce interference to enhance network capacity and/or keep the power consumption at a sustainable level while maintaining acceptable performance.
Power control may also be categorized into downlink power control and uplink power control. Also, there are generally two types of power control, closed loop power control and open loop power control. In closed loop power control, the transmitter sends with a certain power setting and the receiver can send feedback to the transmitter requesting the transmitter to increase or decrease the power. The loop is running in a cyclic matter and several loops may be needed before an optimal power setting is achieved. Open loop power control is used in cases where receiver feedback is considered unfeasible such as during UE initial set up phase. With open loop power control, the transmitter will measure certain signals with known characteristics and choose a power setting it believes has the optimal level.
For example, in Long Term Evolution, LTE, the Physical Uplink Shared Channel, PUSCH, and the Physical Uplink Control Channel, PUCCH, are subject to a combined open and closed loop power control algorithm, i.e. to control the transmission power for uplink physical channels a combination of an open and a closed loop power control procedure is used. The Physical Random Access Channel, PRACH, is subject only to open loop power control.
With the increased complexity of modern network deployment scenarios, power control, like many other network functions, is facing new requirements and challenges. For example, there may be scenarios where the UE may need to increase the uplink power to a level higher that a maximum defined target power, or the UE may need to increase the uplink power further due to interference by another nearby UE.
However, the closed loop power control procedure has some limitations, making it challenging to effectively handle such scenarios. For example, the closed loop procedure introduces extra loops of adjustment of the power, thus increasing the delay to reach proper power settings. It generally needs to apply the change in power settings separately to different physical uplink channels, which introduces considerable complexity. Also, it cannot impact physical channels such as the PRACH, where only open loop power control can be applied.